On a separate day, subjects will be admitted to the General Clinical Research Center (GCRC) of the South Texas Veterans Healthcare System, Audie Murphy Division, San Antonio, Texas, between 6:45 and 8 AM for a hyper-insulinemic euglycemic (80 mU (milli-Unit)/m2•min) clamp. Continuous indirect calorimetry (Deltatrac, Sensormedics, Anaheim, CA) will be performed for 30 minutes prior to the start of the insulin clamp, and during the 150-180 minutes period of the insulin clamp to calculate rates of glucose and lipid oxidation. After obtaining the basal samples for insulin, C-peptide, a priming dose of insulin is given for first 10 minutes which is followed by constant infusion. At 5 minutes a variable rate of glucose is infused to maintain plasma glucose at ~100mg/dl for 180minutes.